set global transaction isolation level REPEATABLE READ;
set global transaction isolation level  READ COMMITTED;
set global transaction isolation level READ UNCOMMITTED;
set global transaction isolation level SERIALIZABLE;

設置會話隔離級別

set session transaction isolation level REPEATABLE READ;
set session transaction isolation level READ COMMITTED;
set session transaction isolation level READ UNCOMMITTED;
set session transaction isolation level SERIALIZABLE;

通過配置文件設置隔離級別

[mysqld]
transaction-isolation = REPEATABLE-READ
transaction-isolation = READ-COMMITTED
transaction-isolation = READ-UNCOMMITTED
transaction-isolation = SERIALIZABLE

查看隔離級別

SELECT @@GLOBAL.transaction_isolation
SELECT @@SESSION.transaction_isolation
show variables like '%iso%';